The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, the electronics industry utilized various methods and structures to form soft-start circuits for power controllers of power supply systems. For example the soft-start circuit of a pulse width modulated (PWM) or other type of switching power supply controller. An example of such a switching power supply controller is the TEA1507 OR TEA1533 supplied by Philips Semiconductors of Eindhoven, Netherlands. Typically the soft-start circuit allowed the current supplied to the load to increase over a given time period while the output voltage was slowly increasing from zero to a desired output voltage value. Often, the first pulse of current that the soft-start circuit allowed the power supply controller to supply to the system was large and successive pulses of current increased from the initial current pulse. One problem with the prior soft-start circuits was that the initial large current pulse produced undesirable audible noise.
Accordingly, it is desirable to have a soft-start circuit that does not create audible noise during the soft-start period of operation of the power supply controller.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention.